Field of the Invention
The present invention relates to an overcurrent protective device, an electronic apparatus having the overcurrent protective device mounted therein, an integrated circuit having the overcurrent protective device integrated therewith, and a signal transmission circuit which transmits a signal from an input terminal to an output terminal via a switch or interrupts such a signal, and particularly to a technology for protecting the electronic apparatus when an internal circuit fails and short-circuits, and a signal transmission circuit and an overcurrent protective device which prevent an erroneous operation of a load by maintaining, at a low voltage, erroneous signal transmission caused by a high temperature leakage current, a noise, and the like.
Description of the Background Art
An overcurrent protective device is known which prevents an overcurrent by limiting a current supplied to a load. For example, Japanese Patent Laying-Open No. 2001-145338 discloses a switching power supply apparatus comprising a first overcurrent protective circuit that performs an overcurrent protective operation once a load current of at least a first overcurrent value which significantly exceeds a rated value flows, and a second overcurrent protective circuit that performs an overcurrent protective operation once a load current of at least a second overcurrent value which exceeds the rated value of the load current by a small magnitude and is thus less than the first overcurrent value flows for a prescribed period of time. According to this switching power supply apparatus, an appropriate overcurrent protective operation can be provided by a simple circuit configuration. Furthermore, for example, Japanese Patent Laying-Open No. 2-241325 discloses an overcurrent protective device of a power supply circuit, that performs an overcurrent protective operation for a load when an overcurrent state continues after a timer circuit's delay time elapses. According to this overcurrent protective device, a protection circuit which alleviates a heat dissipation means can be configured without taking a rush current into consideration.
An electrostatic protective circuit is proposed which uses a clamping circuit for protection of an internal circuit in an electronic apparatus feeding a power supply voltage to a load.
Japanese Patent Laying-Open No. 6-163841 discloses a circuit generating a clamp voltage by a Zener diode connected between a power supply line supplying power to an internal circuit and the ground, to suppress application of a high voltage to the internal circuit connected to the power supply line, to thus protect the internal circuit.
In the invention according to Japanese Patent Laying-Open No. 6-163841, the Zener diode has a cathode connected to the power supply line and has an anode connected to the ground via a resistor. A transistor has a collector connected to the power supply line. The transistor has an emitter connected to a ground line. The transistor has a base connected to the anode of the Zener diode.
According to the above configuration, when an overvoltage is generated, the voltage applied to the internal circuit is clamped by the breakdown voltage of the Zener diode. Furthermore, by this clamp voltage, the transistor conducts, and the current which flows through the power supply line dissipates toward the ground via the transistor.
Japanese Patent Laying-Open No. 2009-99641 discloses a circuit employing a separating resistance that is connected to an input and output terminal to cause a voltage to drop to suppress application of high voltage to an internal circuit connected to an input and output line, to thus protect the internal circuit.
The circuit by Japanese Patent Laying-Open No. 2009-99641 includes a first electrostatic protective circuit, a second electrostatic protective circuit, and a separating resistance. The first and second electrostatic protective circuits pass to the ground a surge current generated by a surge voltage applied to the input and output terminal. The separating resistance protects the internal circuit by dropping the voltage which the internal circuit receives in an early stage of application of the surge voltage.
Japanese National Patent Publication No. 2014-500700 discloses a protection circuit for a lithium battery, that has a configuration providing a clamping circuit between overcurrent protective and short circuit protective circuits and a circuit negative electrode “B−” in order to protect the overcurrent protective and short circuit protective circuits from negative high pressure generated at the circuit negative electrode “B−” when an overcharge protective function is operated and a switch M1 associated with the negative electrode of the lithium battery is brought out of conduction.
When switch M1 is brought out of conduction for overcharge protection and negative high voltage (of −20 V for example) is generated at the circuit negative electrode “B−”, the clamping circuit can limit a negative voltage level of the overcurrent protective circuit and the short circuit protective circuit to a prescribed level (for example, of −2 V to −3 V) and can thus prevent damage to a low voltage MOS component included in the overcurrent protective and short circuit protective circuits.
A signal transmission circuit is proposed which transmits a signal from an input terminal to an output terminal via a switch, that prevents the signal's erroneous transmission.
Japanese Patent Laying-Open No. 2015-15643 discloses a signal transmission circuit connecting a pull-down resistor to a gate of an output transistor forming an open-drain output stage for an output terminal. According to Japanese Patent Laying-Open No. 2015-15643, when a command to drive the output transistor is ceased, the signal transmission circuit pulls the gate terminal of the transistor to the low level by the pull down resistor to prevent signal transmission.